FIG. 4 shows a multi-point light emission type semiconductor laser according to the prior art. In FIG. 4, reference numeral 1 designates a p type semiconductor substrate. N type GaAs current blocking layers 2a and 2b are disposed on substrate 1. P type Al.sub.0.5 Ga.sub.0.5 As first cladding layers 3a and 3b are disposed on blocking layers 2a and 2b, respectively. P type Al.sub.0.15 Ga.sub.0.85 As active layers 4a and 4b are disposed on first cladding layers 3a and 3b, respectively. N type Al.sub.0.5 Ga.sub.0.5 As second cladding layers 5a and 5b are disposed on active layers 4a and 4b, respectively. N type GaAs contact layers 6a and 6b are disposed on second cladding layers 5a and 5b, respectively. Current injection grooves 7a and 7b are provided at current blocking layers 2a and 2b, respectively. Reference numerals 8a and 8b designate light emission points of the laser device. A separation groove 9 is provided between the two light emission points 8a and 8b. N side electrodes 10a and 10b are produced on the contact layers 6a and 6b, respectively. A p side common electrode 11 is provided on the p type GaAs substrate 1. This laser device is provided on the electrically insulating submount 12. Submount electrodes 13a and 13b are provided respectively corresponding to the light emission points 8a and 8b. In this figure, this laser device is a so-called junction down mounted device where the light emission points are close to the heat sink side.
The device operates as follows.
In this prior art device, since the separation groove 9 is reaches the substrate 1, light emission points 8a and 8b are separated and do not have a common n side region. When a forward direction bias is applied between n side electrode 10a and p side electrode 11, a laser oscillation occurs at light emission point 8a, and when a forward direction bias is applied between n side electrode 10b and p side electrode 11, a laser oscillation occurs at light emission point 8b. In this way, the respective light emission points can be driven independently.
Furthermore, this prior art laser device is junction down mounted as shown in FIG. 4, and n side electrodes 10a and 10b are connected with the submount side electrodes 13a and 13b, respectively, but insulated from each other, thereby enabling independent operation of the light emitting points. The heat resistance from the respective light emission points to the heat sink is low and superior heat irradiation is obtained. Therefore, thermal interference between the respective light emission points during operation are greatly improved relative to junction up mounted in which the substrate side is bonded toward the heat sink.
In the prior art multi-point light emission type semiconductor laser device of such a construction, the respective light emission points commonly have the substrate at the p side, and they are not perfectly electrically isolated. Accordingly, the light emission output from one of the light emission points is subjected to variations dependent on the on/off operation of the other light emission point, which results in a severe problem in practical use. Furthermore, when the prior art multi-point light emission type semiconductor laser device is junction down mounted, the solder flows out, and the respective separated electrodes may be electrically short-circuited, thereby resulting in the largest problem in the production of this laser device. Although modifications in the configuration of the submount may be adopted as measures against these problems, these modifications cannot be adopted in junction down mounted multi-point light emission type semiconductor laser devices having more than three light emission points. A method of circulating an electrode so as not to shield the light emission from the rear side laser facet also cannot be used as a solution.